Polyethylene glycol (PEG) is a water-soluble, nontoxic, low immunogenic and biocompatible polymer that has been approved by the FDA for human usage by oral intake or intravenous and subcutaneous injection. Research shows that PEG has effects on preventing the colorectal cancer and healing the neuronal injury. Besides, the macromolecules (such as protein, nano drug and liposome) modified by PEG have the advantages on decreasing their immunogenicity, increasing half-life and biocompatibility. However, there is still no convenient way to effectively quantify PEG or PEG-modified (PEGylated) molecules in vivo.
Current methods used for quantifying PEG include, for example: (a) using the traditional ELISA, also known as the Sandwich Enzyme-Linked Immunosorbent Assay, to directly recognize protein, but the detecting process is hard to be achieved and the results are not precise due to the PEG used to modify proteins often cover the epitope for antibodies to recognize. Moreover, using ascites to produce antibodies has been prohibited by the European Union and the US, and this results the price of products related to ELISA to raise in the future. (b) A colorimetry which use barium-iodide or Fe(CN)3 and PEGylated protein to form a compound need to get rid of other proteins prior to detect, and sensitivity of this method is relatively low, only reach about 1-5 μg/ml. (c) To detect PEG by isotope labeling PEGylated molecule. Although the sensitivity for this method is good, this method can not be used in every PEGylated molecule. Besides, due to the production of radioactive waste, this method can only be performed by specific operators in specific lab, causing inconvenience and leading to unpopularity. Therefore, developing a method which is simple, sensitive, cheap, and able to detect the pharmacokinetics of any PEGylated molecules in vivo can solve those problems caused by traditional methods, such as inconvenience, low sensitivity, and expensive. Also, this new method can be used in any labs, helping labs to evaluate the pharmacokinetics of PEGylated molecules in vivo or in vitro. This method will play an important role in developing PEGylated drug in the future.